🔋 Battery Charge Time Calculator
Estimate how long it will take to charge a battery based on its capacity, your charger’s output current, current charge level, and charging efficiency.
What this calculator does
The Battery Charge Time Calculator estimates how long it will take a charger to bring a battery from its current charge level up to a target level, accounting for the charger’s real-world efficiency.
How the formula works
The energy still needed is the battery’s capacity multiplied by the percentage gap left to charge: Ah Needed = Capacity × (Target% – Current%) ÷ 100. Chargers are never perfectly efficient — some energy is lost as heat — so the calculator reduces the charger’s rated current by an efficiency percentage (commonly 80-90% for lead-acid batteries and somewhat higher for lithium-ion) before dividing: Time = Ah Needed ÷ (Charger Current × Efficiency).
Actual charge times vary because most chargers taper their current as a battery approaches full charge (especially in the final 10-20%), rather than charging at a constant rate the whole time. Treat this result as a useful estimate for planning purposes, and always follow your battery and charger manufacturer’s specific guidance.